1. Field of the Invention
This invention relates to a temperature adjusting device for an LED light source that is provided with an LED light source, a temperature sensor for detecting an ambient temperature of the LED light source, a cooling fan for cooling the LED light source, a driving circuit for driving the cooling fan, and a control unit which controls a voltage to be applied to the cooling fan so as to set the ambient temperature within a predetermined range based upon the results of detection by the temperature sensor.
2. Description of the Related Art
With respect to a light source used in a copying machine, an image-reading apparatus and the like, after turning the light source on, a temperature rise tends to occur due to self heat generation to cause changes in the light source characteristics and the resulting adverse effects in image quality of a read image. For this reason, a device which carries out temperature adjustments so as to adjust the ambient temperature (environmental temperature) of the light source within a predetermined temperature range by using a heater and a cooling fun has been proposed. For example, JP-A No. 2-267541 has been known as such a device using a fluorescent lamp as the light source.
Further, in a photographic processing device for forming photographic prints, a scanner for reading frame images formed in a developed negative film has been used. With respect to a reading light source for use in this scanner, a halogen lamp has been generally used. Here, those light sources using an LED light source have also been known from the viewpoints of its long life and elimination of the need for exchanging the light sources. For example, JP-A No. 2002-365735 has disclosed such a photographic film reading device.
In the case when an LED light-source is used, the LED is subjected to changes in characteristics in the light amount and wavelength depending on temperatures and the subsequent changes in the reading performance; therefore, it is necessary to carry out temperature adjustments. In order to carry out the temperature adjustments, a temperature sensor for detecting the environmental temperature at which the LED light source is placed is installed, and when the preset temperature range is exceeded, a cooling fan is turned on so as to lower the temperature. When the temperature is cooled to a preset temperature, the cooling fan is turned off.
However, the control method for on/off controlling the above-mentioned cooling fan has the following problems. Since, upon turning the cooling fan on, the LED is quickly cooled, the characteristics of the LED tend to deviate. LED light sources of three colors are required in order to read an image of a color photographic film; however, when there are deviations in the characteristics, adverse effects are caused on the reading performances. Moreover, when the cooling fan is quickly turned on and off, changes in noise are offensive to the ear, and make the workers uncomfortable.
When a halogen lamp is used as the light source, a cooling fan is also used; however, since the halogen lamp is less susceptible to changes in characteristics due to the ambient temperature, the cooling fan can be continuously rotated without the necessity of turning on and off. When the cooling fan is continuously rotated, the noise from the fan is not offensive to the ear. In the case of the LED light source, however, since the characteristics thereof are changed depending on the ambient temperature, it is not possible to keep the cooling fan rotating all the time.
The present invention has been devised so as to solve the above-mentioned problems, and its objective is to provide a temperature adjusting device for an LED light source which, upon temperature-adjusting the LED light source by using a cooling fan, neither causes unnecessary deviations in characteristics in the LED, nor makes the workers uncomfortable due to abrupt changes in noise.